Primary and secondary power supplies are often used in tandem to power various forms of application circuitry (e.g., timekeeping). Inputs for primary power supplies have typically been electrically coupled to system power sources and inputs for secondary power supplies have been electrically coupled to back-up power supplies (e.g., batteries), neither of which were rechargeable (e.g., rechargeable batteries). The power management circuitry used to control power supplies have not allowed convenient mechanisms or methods that allow users to access and/or recharge batteries that are used as a power supply. As a result, a user's choice has been rather limited. The user could use only the system power supply (e.g., for the first power source) and non-chargeable batteries for the primary and secondary power supplies. Alternatively, if the user insisted on rechargeable batteries, external charging circuitry was required, because necessary circuitry (if it existed at all) could not be easily integrated into an integrated circuit. As referenced above, a reliable power supply is an especially important consideration in time-keeping applications, because users generally want to perpetually save, back-up, and otherwise preserve timekeeping information (e.g., what time is it?). However, it is important in other applications as well.
In addition, adding features to existing product lines introduces additional factors, such as compatibility issues. New generations of parts are preferably compatible with previous generations of parts. As a result, new features, such as those discussed above, need to be able to be added to or integrated with existing systems without altering the basic functionality or operation of previous generations of electrical devices (e.g., integrated circuits). For instance, when there are a limited number of pins, one simply cannot add an extra pin to invoke or activate the newly added feature. Thus, it complicates the addition of new features without affecting the basic functionality.